Filament transformers for portable X-ray inspection units

ABSTRACT

A high voltage step-up transformer incorporating dual insulating layers, a relatively thick, heat-resistant &#34;TEFLON&#34; layer exhibiting extremely low dielectric losses and a thinner epoxy layer having a tractive, non-skid outer surface supporting a large plurality of fine wire secondary winding turns.

This is a divisional of application Ser. No. 07/860,004 now U.S. Pat.No. 5,385,161 filed on Mar. 30, 1992.

This invention relates to unusually lightweight portable X-ray machinesof the kind used in industrial noninvasive inspection for defects,discontinuities, voids or cracks in manufactured products or machinessuch as aircraft fuselages, jet aircraft engines or other products. Moreparticularly, this invention relates to such portable X-ray units whichmay be conveniently stored and moved over long distances, and deployedin the field with ease and convenience to perform such X-ray examinationof vehicles, tanks, piping, structures, machines or other devices atsuccessive different locations.

BACKGROUND OF THE INVENTION

Conventional portable X-ray equipment is heavy, bulky and inconvenientto move and deploy for use. The high voltage required to operate theX-ray tube customarily requires extremely large and heavy electricalcomponents to provide the desired stepped up direct current drivingvoltage for the X-ray tube. For this reason, operation of X-rayinspection equipment in the field has involved considerableinconvenience for the user. Consequently, a significant need hasdeveloped for lightweight, portable X-ray inspection equipment which canbe readily stored, transported, deployed and used at successivedifferent field locations.

BRIEF SUMMARY OF THE INVENTION

The devices of the present invention have proved highly useful inproviding ample X-radiation for X-ray inspection purposes in the field,while requiring extremely lightweight and convenient control circuitryand cooling unit subassemblies, all easily portable. The electricalcircuitry and systems incorporated in the devices of this invention arebelieved to exemplify several unique features, and the use of a highfrequency input signal, preferably at about 25 kHz, for a multi-stagevoltage multiplier, producing a 160 kV DC output voltage, achievesunexpectedly smooth, unvarying DC output with no more than 1% variationin voltage. The precise DC voltage produced is controlled within closetolerances, utilizing unique control circuitry and a voltage dividerfeedback loop.

In parallel with the multi-stage voltage multiplier is a multi-stagefilament transformer producing very low amperage AC filament heatingoutput currents for the X-ray tube filament. By operating at an evenhigher frequency, preferably about 33 kHz, very lightweight transformerstages are employed in this filament transformer array, and circuitnoise or crosstalk between the high voltage DC multiplier stages and thefilament transformer stages can be reduced to a minimum or virtuallyeliminated.

By utilizing this multi-stage, preferably a five-stage, filamenttransformer, maximum voltage between the primary and secondary windingsof each transformer stage is limited to 32 kV, thus reducing thedielectric volume and weight of the insulation between transformerwindings. In the same manner, the five-stage voltage multiplier alsolimits the voltage between successive stages to 32 kV, permittingminimum size, volume and weight of insulation and capacitive dielectricmaterial employed in the voltage multiplier components.

Each stage of the voltage multiplier employs three capacitors and eightseparate diodes. The input transformer employed to provide the steppedup AC input voltage of 500 volts delivered to the five-stage voltagemultiplier incorporates a unique transformer winding tube withunexpectedly useful properties. The secondary winding of each filamenttransformer stage, connected to the primary winding of the nextsucceeding stage, has its DC potential matched to that produced by thecorresponding stage of the DC voltage multiplier, by being connected tothe corresponding interstage junction of the multiplier. A unique formof clamping connector is incorporated joining the smoothly roundedcomponents in these assemblies to assure sound reliable electricalconnections while minimizing arcing or corona discharges, and thisunique connector cooperates with the threaded interconnection betweensuccessive ceramic insulated capacitors in the voltage multiplier toproduce an unusually lightweight multiplier forming a sturdy structuralcomponent of a unified combined multiplier filament transformercombination.

A companion device employed with the portable X-ray systems of thisinvention is a laser target selector attachment, easily fitted on theanode end of the X-ray tube and uniquely adapted to seat thereon andproject a narrow laser beam in the direction of the axis of theX-radiation emitted by the X-ray tube. This laser target selector easilyand conveniently permits the user to adjust the position of the portableX-ray tubehead in the systems of this invention for extremely accurateaiming, and for positioning of an X-ray film holding cassette.

Accordingly, a principal object of the present invention is to providelightweight and highly effective X-ray inspection units which are easilystored, transported, deployed and used in the field at differentsuccessive inspection sites.

A further object of the invention is to provide such X-ray inspectionunits having an X-ray tubehead mounted on an easily moved portable standand connected to portable control and portable cooling portions of theassembly by cables and cooling liquid conduits.

Another object of the invention is to provide such portable X-rayinspection units incorporating X-ray tubeheads which are unusuallycompact, small and comparatively light in weight.

Another object of the invention is to provide such portable X-rayinspection units which are capable of providing high voltage DCoperating potential for the X-ray tube in the neighborhood of 160 kVwith minimum voltage variations.

Still another object of the invention is to provide such portable X-rayinspection units exhibiting minimum cross talk or interference betweenthe filament heating AC voltage applied to the filament of the X-raytube, and the high voltage DC operating potential applied betweencathode and anode of the X-ray tube.

A still further object of the invention is to provide such portableX-ray inspection units incorporating electrical components of unusuallylight weight and sturdy design.

Still another object of the invention is to provide such portable X-rayinspection units having lightweight power supply and filamenttransformer circuitry enclosed together with the other lightweightelectrical components and the X-ray tube in a compact tubehead ofcomparatively small size and light weight.

A further object of the invention is to provide such portable X-rayinspection units with power supply components connected together bysturdy, compact and easily operated connectors.

Another object of the invention is to provide such portable X-rayinspection units equipped with a laser target selector which is readilymounted on the X-ray tubehead itself, and easily aimed and observed tofacilitate the selection of target areas for the X-ray inspection to beperformed.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the features of construction,combinations of elements, and arrangements of parts which will beexemplified in the constructions hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description taken inconnection with the accompanying drawings, in which:

FIG. 1A is a perspective view showing a portable X-ray inspection unitof the present invention including a lightweight X-ray tubehead mountedon a tripod stand with a digital power supply control unit and a coolingunit in the background.

FIG. 1B is a similar perspective view of an air cooled industrial X-rayinspection unit of the present invention with an analog control unit inthe foreground;

FIG. 2 is a schematic block diagram of the X-ray inspection system shownin FIG. 1A;

FIG. 3 is a schematic block diagram of the air cooled X-ray inspectionunit shown in FIG. 1B with its control unit;

FIG. 4 is a block diagram of the components incorporated in each of theblocks of the block diagram illustrated in FIG. 2;

FIG. 5 is a schematic diagram of the components incorporated in thetubehead portion of the X-ray inspection units illustrated in theprevious figures;

FIG. 6 is a fragmentary front elevation view of the voltage multiplierportion of the circuitry components mounted inside the tubeheadillustrated schematically in FIG. 5;

FIG. 7 is a partial cutaway view of the capacitors and diodes arrayedbetween upper and lower support plates in the assembly shown in FIG. 6;

FIG. 8 is a fragmentary side elevation view showing one of the columnarray capacitor assemblies and the filament transformer assembly in thevoltage multiplier of FIG. 6 with the other two column array capacitorassemblies being removed for clarity;

FIG. 9 is a cross sectional elevation view of the tubehead of FIG. 1Aand FIG. 2 with the voltage multiplier assembly of FIG. 6 being shown inits installed position inside the tubehead, together with the X-ray tubeand its cooling manifold and connections;

FIG. 10 is a top plan view of the tubehead of FIG. 9;

FIG. 11 is a top plan view of a laser target selector suitable for usewith the tubehead of FIG. 9;

FIG. 12 is a fragmentary schematic view showing the laser targetselector of FIG. 11 installed in its position in contact with theberyllium window at the anode X-ray emitting portion of the X-ray tubeof FIG. 9;

FIG. 13 is a perspective view showing the construction of the lasertarget selector attachment of FIGS. 11 and 12;

FIG. 14 is a fragmentary exploded elevation view of two capacitors andtheir connecting components from a capacitor column array as shown inFIGS. 6-9.

FIGS. 15 and 17 are top plan views of multiprong clamping connectorsutilized in the assembly of FIGS. 9-14;

FIGS. 16 and 18 are corresponding side elevation views of the connectorsshown in FIGS. 15 and 17 respectively; and

FIG. 19 is a side elevation view, partially in cross section, of one ofthe two segments of the high voltage step up transformer providing inputvoltage to the first stage of the DC voltage multiplier.

BEST MODE FOR CARRYING OUT THE INVENTION

The circuitry illustrated schematically in FIGS. 4 and 5 produces thedesired DC operating potential across the electrodes of the X-ray tube36, employing a high voltage DC power supply 38 including the highvoltage step up transformer 68, a multistage high voltage rectifiermultiplier 70 and a voltage divider 71 in parallel with the multistagemultiplier 70 with control circuitry maintaining the DC output voltageof the multiplier at a constant DC level within extremely closetolerances.

The input transformer 68 receives a square wave input at a frequencypreferably between 22 and 28 kHz, and desirably at a frequency ofsubstantially 25 kHz. In parallel with the multiplier 70 inside theX-ray tubehead 30 enclosing the multiplier and the X-ray tube 36 thereis provided a filament step down transformer 40 which is also subdividedinto a plurality of stages corresponding to the number of stagesemployed in the multiplier 70. In the figures, a five-stage multiplier70 and a five-stage filament transformer 40 are illustrated withinterstage junctions in each of these arrays respectively joinedtogether by electrical conductors maintaining the interstage junctionsat the same DC voltage levels for multiplier 70 and transformer 40. Eachof these successive levels is nominally 32 kV DC above the potential ofthe previous interstage junction, so that each of the plurality of fivestages illustrated in the figures has a limit potential of 32 kV overits two terminal junctions. The filament drive conductor 64 deliveringAC input voltage to the filament transformer 40 is provided by controlunit 32 with an AC input voltage at a frequency preferably between 30and 36 kHz, and most desirably at a frequency of substantially 33 kHz.By this means, crosstalk and noise between the respective 25 kHz and 33kHz frequencies of the multiplier 70 and the filament transformer 40 areminimized or eliminated.

These relatively high operating frequencies for the two multistagearrays permit the use of unusually small, compact and lightweightcomponents in these two arrays, as hereinafter described. The componentsforming the high voltage DC multiplier delivering nominally 160 kVpotential to the electrodes of the X-ray tube 36 are shown schematicallyin FIG. 5 and also in the assembly views of FIGS. 6, 7, 8 and 9. Asshown in these figures, the five-stage multiplier of FIG. 5 employsfifteen ceramic insulated capacitors arrayed and anchored together inthree generally vertical columns, sturdily anchored together between alower mounting plate 201 and an upper mounting plate 202.

This entire multiplier assembly 70 is supported via bottom plate 201between four substantially vertical insulator stringer bars 203, bestseen in FIG. 6 and FIG. 9, whose lower ends are mounted by machinescrews 204 to a sturdy metal bottom end plate 206. Lower mounting plate201 is spaced upward above bottom end plate 206 by a distance sufficientto accommodate the high voltage step up transformer 68 providing inputvoltage to the multiplier 70 as shown in FIG. 6. Nylon screws 207passing through bars 203 are threaded radially into tapped radial holesformed in the edge of lower mounting plate 201, sturdily positioning theentire multistage multiplier assembly 70 in position.

The upper ends of bars 203 are secured to an annular tube socket 208 inwhich the X-ray tube 36 is mounted, as indicated in FIGS. 6 and 9.Bottom end plate 206 thus forms the lower end of tubehead 30 and anannular X-ray tube support plate 209 firmly positions the upper end oftube 36 at the upper end of tubehead 30. An external X-ray port shield211 protrudes upward from the upper end of tubehead 30, enclosing theextended upper end of tube 36. Shield 211 is provided with a port 212,through which X-rays produced in tube 36 are delivered through aberyllium window to the target along a radiation axis 213.

The cutaway views of FIGS. 7 and 8 illustrate the construction of themultistage voltage multiplier 70 and the adjacent positioning of thefilament transformer assembly 40 with the interstage junctionconnections between both of these arrayed multistage assemblies 40 and70.

The three columns of five Ceramite® ceramic insulated capacitors,securely anchored together in column arrays, are illustrated in FIGS. 7and 8. FIGS. 8 shows the central capacitor column 214 composed of fiveidentical capacitors 216 of 440 pf. These capacitors 216 form thecentral capacitor column shown in FIG. 8 and also in FIG. 5, and thesame 440 pf capacitors 216 comprise the top two capacitors of each ofthe two outer five-capacitor columns 234, as shown in FIGS. 4 and 7. Inthese two flanking outer capacitor columns, the next two lowercapacitors in each column are 700 pf capacitors 217, and the lowermostcapacitor in each of these two outer flanking columns is a 1300 pfcapacitor 218, notably larger in size than the other capacitors.

The terminal connections of these ceramic insulated capacitors 216, 217and 218 are formed as internally threaded ferrules 219 protrudingaxially from each end of the cylindrical ceramic insulated capacitors,as indicated in FIG. 14. Each capacitor is joined to the next adjacentcapacitor by a threaded rod 221. As indicated in the exploded view ofFIG. 14, a multiprong connector 222 or a dual prong connector 223 isprovided with a stepped mounting bore 224 passing through one endaccommodating threaded rod 221, with enlarged portals 226 at each end ofmounting bore 224 each accommodating a lock washer 227. Thus, asindicated in FIG. 14, a connector 222 or 223 is loosely mounted onthreaded rod 221, which extends through its bore 224. Sandwiched betweenthe connector and the adjacent ceramic insulated capacitor in whichthreaded rod 221 is threadedly inserted is a lock washer 220.

Thus, FIG. 14 shows that a sandwich construction of two lock washerswith a connector between them, all mounted on threaded rod 221, isinterposed between each adjacent pair of capacitors, whose threadingassembly on threaded rod 221 clamps lock washers 227 within portals 226between connector 222 or 223 and the threaded ferrule 219 of theadjacent capacitor.

Inserted between the prongs of each of the connectors 222 and 223 is aconnector sleeve 228 which slides between and fits with close tolerancesinto the slots between adjacent prongs 229 of the connector 222 or 223.Connector sleeve 228 is dimensioned to receive insulation-strippedconductor wire 231. As indicated in FIG. 8, one or two strippedconductor wires 231 may be inserted and soldered in each sleeve, andthereby electrically connected between the prongs of the connector 222or 223 which are clamped together on the sleeve to complete theelectrical connection by the insertion of a threaded set screw 232.Connectors 222 and 223 are preferably made of resilient brass, which isnot stressed beyond its elastic limit but is deformed sufficiently bythe insertion and tightening of the set screw 232 that the prongs 229are flexibly drawn together to provide excellent electrically conductiveclamping attachment of sleeves 228 and conductors 231 with connector 222or 223.

The connectors and capacitors shown in the disassembled exploded view ofFIG. 14 are shown assembled in the overall assembly of the centralcapacitive column array in FIG. 8, where connectors 222 are easilyvisible sandwiched between each adjacent pair of capacitors 216. Thefour prong connectors 222 are well suited for this purpose because ofthe sheer number of electrical conductors joined to each other at theinterstage junctions between capacitors in the array 214. As indicatedin FIG. 5, two capacitor terminals and five separate conductor wires areall joined together at each of the interstage junctions of themultiplier 70.

The five conductor wires which are joined at each interstage junction ofthe multiplier 70 include the bridging conductors 231 extending betweenthe filament transformer assembly 40 and the central capacitor column214, as clearly shown in FIG. 5 and FIG. 8, and also the conductor wireextending from each of the diode strings into these interstagejunctions. A total of forty high voltage rectifier diodes 233 arearrayed in the pattern clearly indicated in FIG. 5 in a manner believedto be relatively conventional for high voltage multistage multipliers.

The dual prong connectors 223 are also well adapted to receive twoinsulation stripped conductive wires inserted in a central sleeve 228which is sandwiched between the two prongs 229 of the connector 223 andsecurely held in position by its set screw 232. These dual prongconnectors 223 are well adapted to join the conductor wires from eachdiode string to the junction between the ceramic insulated capacitorsarrayed forming the two outer columns 234, flanking the central column214, and the junction connections are made in the same way illustratedin FIGS. 8 and 14, with the connectors being clamped solidly betweeneach adjacent pair of capacitors threaded on the threaded rod 221, witha lock washer 220 sandwiched between each connector and the adjacentcapacitor. The three capacitor columns 214 and 234 are clearly shown inFIG. 7, where the diode strings are also clearly illustrated as well asthe two-prong connectors 223.

Filament Transformer

The filament transformer 40 is clearly shown in FIG. 8. Five ferritetoroid cores 236-240, preferably coated with epoxy paint, are shownarrayed vertically up the left side of FIG. 8. For DC potentialmatching, the lowermost core 236 is connected to the core of highvoltage step-up transformer 68 supplying input AC voltage to themultiplier 70, and both of these connected cores are also connected toground, all as shown in FIG. 4. The ground connection is provided by aconductor 241 joined by a soldered connector plate to a surface of theferrite core 236 from which the epoxy paint has been sanded away.

First primary winding 242 comprises thirty-six turns of No. 22 AWG wire,wound around core 236. The first secondary winding 243 is formed by aconsiderably larger coil of six turns of RG 58 wire, havingapproximately a 2" outer diameter, wound through the center of core 236and also through the center of second core 237, as indicated in thelower portion of FIG. 8. Both ends of winding 243 are carried across theassembly to be connected to multiprong connector 222 between the twolowermost capacitors 216 in central capacitor stack 214, as shown inFIGS. 5 and 8.

A cylinder of Teflon tubing 0.030" in thickness lines the interior ofall five toroid cores 236-240, and the larger windings such as winding243, are directed through the interior of each of these Teflon tubingcore liners.

The second secondary 246 which also forms the third primary winding isformed as six turns of No. 20 AWG wire, wound over a thin layer ofKapton acrylic tape encircling cores 237 and 238. As indicated in FIG.5, a conductor 231 is joined to this secondary winding 246 and also tosanded off portions of cores 237 and 238 assuring that all three ofthese components are connected to the second interstage junction ofmultiplier 70 and thus maintained at its nominal negative DC potentialof -64 kV. Teflon tubing liner 244 is mounted overlying the six turns ofwinding 246 and the third secondary and fourth primary winding is formedby a second large six turn loop 247 of RG 58 wire, passing through core238 and also through core 239, with conductors 231 from both of its endsleading to another multi-prong connector 222 between the third andfourth capacitors 216 and capacitor column 214. Finally, the fourthsecondary and fifth primary winding is formed by another six turns ofNo. 20 AWG wire underlying Teflon tubing core liners 244, wound throughboth of the adjoining ferrite cores 239 and 240, with a conductor 231joining both cores 239 and 240 as well as this winding 248 to amulti-prong connector 222 between the fourth and fifth capacitors 216 ofthe capacitor stack 214. The final or fifth secondary winding 249 of thefilament transformer array 40 is formed by four turns of RG 58 wireagain having approximately a 2" outer diameter, wound through the centerof the core liner 244 in core 240, and has one end connected by aconductor to the topmost multi-prong connector 222 overlying theuppermost capacitor 216 in the center stack 214, with the other end ofwinding 249 being connected to the filament of tube 36, as shown in FIG.5.

The ferrite toroid cores 236-240 are shown in FIG. 8 supported in afilament transformer mounting frame 251, formed as an elongated bar withcutouts receiving the ferrite cores. The outer rear surface of themounting frame 251 is shown in FIG. 6, extending upward between the twonearest insulator stringer bars 203. The large size of the windings 243,247 and 249 and the open space inside the Teflon tubing core liners 244as well as the exposure on all sides to the surrounding atmosphereprovide excellent convective and radiation cooling for the variouscomponents of the filament transformer 40.

Mounting frame 251 itself provides the elongated outer surface shown inFIG. 6 which conveniently radiates accumulated heat to the outer shellof tubehead 30, as shown in FIG. 9, where the left-hand portion of thisouter shell is illustrated as a cooling manifold 252 having a coolanttubing union connection 253 at its lower end and a similar connection254 at its upper end joined to cooling tubes 256 employed for coolingthe X-ray tube 36. Inside X-ray port shield 211 the manifold 252 is wellpositioned to provide heat transfer and cooling for the shell oftubehead 30 in the case of the unit illustrated in FIG. 1A and 2 where acooler unit 34 provided with the hose connections 257 leading to thetubehead is an integral part of the overall system.

The tubehead of FIG. 3 is air cooled by an internal fan not illustratedin the figures. Twin hoses 257 shown in FIG. 2 deliver the coolant fluidfrom the cooler unit 34 to the tubehead 30 in the systems of FIGS. 1Aand 2.

The size of the components illustrated in FIGS. 6, 7 and 8 may bevisualized by reference to the smallest of the ceramic insulatedcapacitors 216 which measure approximately 3 centimeters in diameter andjust over three centimeters in length. The tubehead dimensions areapproximately 28 inches in length and just over 7 inches in diameter,with an approximate weight of 25 lbs. The unusually high frequency ofthe driving voltages employed both in the multiplier and the filamenttransformer can be credited with the very significant weight reductionscompared to conventional X-ray inspection units, which are achieved bythe devices of the present invention. The use of aluminum and structuralplastic parts also contributes to this highly desirable weightreduction.

High Voltage Step Up Transformer

Transformer 68 supplying input voltage to the DC voltage multiplierarray incorporates a unique winding tube construction. The centralcylindrical tube 258 on which both primary and secondary windings arecarried incorporates a unique construction. A centralplastic-impregnated or coated paperboard cylinder 259 has the heavyprimary winding 261 applied thereto. A relatively thick outer layer 260preferably of Teflon forms an insulating layer directly overlying theprimary winding. Teflon is preferable and uniquely useful for thispurpose because of its extremely low dielectric losses, high dielectricstrength and significant resistance to heat degradation. In some casespolypropylene can be used in place of Teflon, because of its lowdielectric losses. Teflon presents the disadvantage, however, of beingso unusually smooth that the application of the secondary winding 262thereon would be impossible.

For this reason, a thinner outer layer of G10 epoxy forms the outersurface of the winding tube, and this epoxy outer layer 263, whilehaving less dielectric strength and resistance to heat degradation,nevertheless provides the outermost tractive layer of the winding tube,permitting two secondary windings 262 to be firmly anchored on theoutside of the epoxy layer 263.

As indicated in FIG. 6, two input transformer assemblies 68 are rubberblock shock-mounted between the lower mounting plate 201 and the bottomend plate 206, providing the highly satisfactory dielectric strengthrequired for the voltage differential between the primary and secondarywindings, while assuring minimum weight for the transformer components68. The central portion of the resulting winding tube in assembly 68 isof amply large diameter to accommodate a laminated core structure, notshown in the drawings.

FIGS. 6, 7, 8 and 14-18 all illustrate the preferred rounding of edgesand corners of all components involved in the production of highvoltages in order to minimize the developments of arcs or coronadischarges from any remaining sharp corners or edges. It will be noticedthat the ceramic capacitors, the connectors 222 and 223, the tube socket208 and the insulator stringer bars 203 all incorporate rounded, smoothcorners, edges and ends. All of these components in tubehead 30 are thuswell adapted to minimize corona losses.

Laser Target Selector

A removable attachment which has been found to be highly useful with theindustrial X-ray inspection units of the present invention is the laseraimer or target selector 264 illustrated in FIGS. 11, 12, and 13. Asillustrated in FIG. 11, the target selector includes a very smalltubular laser 266 having a radially extending mounting plate 267 mountednear its rear end, and a power cord 268 leading to a battery case 269enclosing a 9-volt transistor battery, with a switch 271 and an on/offindicator lamp 272 beside switch 271. A pair of bails or attachmentrings 273 are mounted at opposite diametric positions on plate 267 closeto its edge, extending in the rearward direction away from the laser'sprojection axis 274. A flexible tension coil spring 276 has each of itsends secured to one bail 273, forming the assembly and shown in FIG. 11.This allows the spring to be stretched as the laser aimer 264 is loweredfrom above over the end of X-ray port shield 211 and cooling tubes 256,bringing the rear end of laser 266 into alignment with port 212. Therespring 276 draws the laser 266 rearward until its rear end rests firmlyagainst the beryllium window 265 through which X-radiation is deliveredby X-ray tube 36 through port 212 as shown in FIG. 12. In this firmseated condition, secured by spring 276, the laser 266 can be switchedon by actuating switch 271, and the laser beam projecting along thelaser projection axis 274 can be observed by the user striking theobject at which the laser is aimed.

Consequently, the tubehead 30 can be readjusted on its tripod andprecisely positioned to bring the laser beam into close alignment withthe target to be inspected. With the laser in this installed position,the laser beam axis 274 substantially coincides with the X-rayprojection axis 213, as indicated in FIG. 12, and after positioningtubehead 30, the detachable laser target selector 264 may be removedmerely by stretching spring 276 and withdrawing the device 264 upwardfrom the end of the port shield 211, exposing the target area for thedesired X-ray inspection.

It will thus be seen that the objects set forth above, and those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanydrawings shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:
 1. A high voltage step-up transformer incorporatingacentral hollow tubular insulator cylinder dimensioned to receive aferromagnetic core extending therethrough; a primary winding ofcoarse-diameter wire helically wound on said insulator cylinder, anouter heat-resistant insulating layer of a polymer, selected from thegroup consisting of polytetrafluorethylene and polypropylene directlyoverlying in connection with and surrounding said primary winding, arelatively thin outer insulating layer of epoxy overlying said polymerlayer, providing a tractive non-skid outer surface, and secondarywinding means comprising a large plurality of turns of relatively finediameter wire helically would on said epoxy layer's outersurface,whereby a precise number of secondary turns can be readily woundon said surface, producing an economical, efficient and lightweight highvoltage transformer.
 2. A high voltage step-up transformer comprising:aferromagnetic core; a cylindrical insulator tube surrounding theferromagnetic core; a primary winding helically wound on the cylindricalinsulator tube; a first heat-resistant, insulating layer, directlyoverlying in contact with the primary winding combining thecharacteristics of low dielectric losses, high dielectric strength andsignificant resistance to heat degradation; a second layer on the firstlayer having a tractive, non-skid surface; a secondary winding helicallywound on the tractive, non-skid surface.
 3. The high voltage step-uptransformer defined in claim 2, wherein the first layer furthercomprises a smooth polymer selected from the group consisting ofpolytetrafluorothylene and polypropylene.
 4. The high voltage step-uptransformer defined in claim 2, wherein the second tractive, non-skidlayer is epoxy.
 5. The high voltage step-up transformer defined in claim2, wherein the first layer further comprises a smooth polymer selectedfrom the group consisting of polytetrafluroethylene polypropylene andthe second layer is epoxy.
 6. A high voltage step-up transformercomprising:a ferromagnetic core; a cylindrical insulator tubesurrounding the ferromagnetic core; a primary winding helically wound onthe cylindrical insulator tube; a smooth polymer first heat-resistant,insulating layer directly overlying in contact with the primary windingcombining the characteristics of low dielectric losses, high dielectricstrength and significant resistance to heat degradation; a tractive,non-skid second polymer layer on the smooth polymer first layer; asecondary winding helically wound on the tractive, non-skid secondlayer.
 7. The high voltage step-up transformer defined in claim 6,wherein the polymer of the smooth polymer first layer further comprisesa polymer selected from the group consisting of polytetrafluroethyleneand polypropylene.
 8. The high voltage step-up transformer defined inclaim 6, wherein the tractive, non-skid second layer is epoxy.
 9. Thehigh voltage step-up transformer defined in claim 6, wherein the polymerof the smooth polymer first layer further comprises a polymer selectedfrom the group consisting of polytetrafluorethylene and polypropyleneand the tractive, non-skid second layer is epoxy.